Acceleration = (change in speed) / (time for the change)
Change in speed = (speed at the end) - (speed at the beginning).
Change in speed = (10 m/s) - (zero) = 10 m/s
Time for the change = 3 sec
Acceleration = (10 m/s) / (3 sec)
Acceleration = (3 and 1/3) m/s² or 3.333 m/s²